This invention relates to an opto-electronic device and more particularly to a visible light semiconductor laser having a wide lasing wavelength range.
Semiconductor lasers having a shorter lasing wavelength have been required mainly in the technical field of optical information processing. However, the AlGaAs/GaAs system which is now prevalently used can not easily provide lasing at the wavelength lower than 720 nm due to its bandgap value. Thus, the AlGaInP/GaAs system laser has been noticed in place of the AlGaAs/GaAs system and will be put to practical use in the near future. However, this material also, due to its bandgap value, can not easily provide the lasing of yellow, green, blue, etc. at the wavelength lower than 600 nm. This AlGaInP/GaAs system is now generally considered to be a material which can provide the shortest wavelength lasing among III-V alloy semiconductor materials, as disclosed in J. Appl. Phys. Vol. 58, 1982, page 4928. This means that the semiconductor laser using the ordinary III-V alloy semiconductor material can not provide lasing at a wavelength lower than 600 nm, i.e. the lasing of yellow, green, and blue other than red.
On the other hand, development of crystal growth such as MBE (Molecular Beam Epitaxy), OMVPE (Organo Metallic Vapor Phase Epitaxy), etc. has enabled the layer thickness in an atomic layer to be controlled. FIG. 1 shows schematic diagrams of the atomic arrangement on the column III sublattice of an Al.sub.0.5 Ga.sub.0.5 As alloy semiconductor and of an atomic layer superlattice semiconductor in which AlAs and GaAs are piled in each monolayer which is hereinafter referred to (AlAs).sub.1 (GaAs).sub.1. As understood from this figure, the superlattice semiconductor having a period on the order of an atomic layer thickness is different from an alloy semiconductor having equivalently the same composition in their electronic energy structure, i.e., bandgap, since they have the same average composition but different short range orders and symmetries. For example, J. P. van der Ziel et al report in J. Appl. Phys. Vol. 48, 1977, page 3108 that in the AlGaAs/GaAs system, the atomic layer superlattice semiconductor has a bandgap greater than the alloy semiconductor by about 100 meV. T. Nakayama et al. report the theoretical analysis of this phenomenon in J. Phys. Soc. Jpn. Vol. 54, 1985, pages 4726-4734.